The present invention relates generally to electrical discharge machines and in particular to apparatuses and methods for performing high-speed, accurate, electric discharge machining operations. The present invention further relates to apparatuses, processes and methods for efficiently programming and operating electrical discharge machines.
An electrical discharge machine (EDM) utilizes a repetitious train of electroerosive sparks or discharges to machine an electrically charged workpiece. In operation, an electrode and the workpiece are brought into proximity with one another, and a dielectric fluid is introduced in the gap therebetween. Typically, the gap between the electrode and workpiece is on the order of approximately 0.1 millimeters to approximately 0.5 millimeters. A power supply connected between the electrode and the workpiece produces a controlled train of direct current (DC) voltage pulses. At a critical value of the applied voltage, the dielectric fluid between the electrode and the workpiece breaks down, and at least partially ionizes causing a series of sparks to be produced. Each spark vaporizes a small quantity of the workpiece creating a tiny pit or crater on the workpiece surface. In addition to assisting in the formation of the spark discharges, the dielectric fluid cools the workpiece during repeated spark discharges and carries away material eroded from the workpiece.
EDM machines are currently used for a large and increasing number of applications because EDM machines are generally capable of machining conductive materials that exhibit high hardness such as carbides. EDM machines can also machine conductive materials that exhibit high tensile strength, or are of otherwise poor machineability. For example, materials that are particularly thin or brittle may be machined using EDM even though conventional drilling, machining, or grinding would otherwise damage the workpiece. However, one complete EDM drilling operation is typically a slow process due to the minute amount of material that is removed from the workpiece during a single spark discharge. Accordingly, typical EDM machines are not fast enough for a number of production-paced applications. Further, EDM machines typically do not provide a flexible architecture suitable for certain automated machining operations. For example, a typical EDM machine has a limited number of axes of motion. Accordingly, an operator of an EDM machine may have to manually reposition a workpiece numerous times to complete the machining that a workpiece requires. The manual intervention of an operator is inefficient, time-consuming, and can potentially lead to increased likelihood of misalignment, or out of tolerance machine operation.
The present invention provides electrical discharge machines that are capable of a relatively wide range of flexibility and range of motion for performing electrical discharge operations. For example, an electrical discharge machine according to at least one embodiment of the present invention can optionally comprise up to, and in excess of six axes of motion. To effectively remove the swarf that is generated during electroerosion operations, the present invention optionally provides both a primary and an auxiliary flushing system. The auxiliary flushing system is used to direct dielectric fluid towards the workpiece external to the electrode. The present invention also provides methods of performing high speed electrical discharge machining operations including determining the zero set conditions that indicate initiation of the electroerosion process.
According to one embodiment of the present invention, a method of performing an electrical discharge machine operation includes advancing an electrode toward a workpiece. At least while the electrode is being advanced towards the workpiece, monitoring of a power supply coupled between the electrode and the workpiece is carried out to detect a draw of current from the power supply as a result of a spark between the electrode and the workpiece. Also, monitoring of the motion of the electrode is carried out to detect dither of the electrode as a result of the spark. A zero set operation is performed if both the draw of current from the power supply and the dither of the electrode is detected, otherwise, the electrode is allowed to continue to transition towards the workpiece. After performing the zero set operation, a desired machining operation is performed.
According to another embodiment of the present invention, a method of performing an electrical discharge machine operation includes advancing an electrode toward a workpiece. At least while the electrode is being advanced towards the workpiece, monitoring of the motion of the electrode is carried out to detect dither in the travel of the electrode. A zero set operation is performed if dither of the electrode is detected, otherwise, the electrode is allowed to continue to transition towards the workpiece. After performing the zero set operation, a desired machining operation is performed.
According to another embodiment of the present invention, an electrical discharge machine includes an actuator and an electrode holder secured to the actuator arranged to selectively transition therealong, the electrode holder further arranged to receive and secure an electrode for unitary motion therewith. A drive device is coupled to the actuator, and a position sensor is communicably coupled to at least one of the drive device and the actuator. The drive device is arranged to provide a position signal that may be interpreted to determine the position of the electrode holder along the actuator. The position signal is communicably coupled to a controller. A power supply is arranged to be coupled between the electrode and a workpiece. A shunt sensor is communicably coupled between the power supply and the controller, the shunt sensor arranged to detect a draw of current therein.
An electrical discharge machine according to yet another embodiment of the present invention includes a base that supports a first table. The first table is arranged to selectively transition in a generally horizontal plane defining a first axis of motion and a second axis of motion generally orthogonal to the first axis of motion. A rotary table is releasably securable to the fist table, the rotary table arranged to selectively rotate about a generally vertical axis defining a third axis of motion. A column extends generally vertically from the base and supports a head unit secured thereto, the head unit arranged to selectively transition generally vertically along at least a portion of the column defining fourth axis of motion. A spinner unit having a generally elongate body is coupled to the head unit for unitary movement along the fourth axis of motion therewith, the spinner unit is further arranged to selectively rotate about a fifth axis of motion generally perpendicular to the fourth axis of motion.
A burning bead is secured to the elongate body of the spinner unit for unitary rotational movement about the fifth axis of motion therewith, the burning head further arranged to selectively transition along a sixth axis of motion defined along the length of the generally elongate body of the spinner unit. An electrode holder is coupled to the burning head and is arranged to receive an electrode therein. A first controller is arranged to selectively control the first, second, third, fourth, fifth, and sixth axes of motion of the electrical discharge machine in a manner to align the electrode with a workpiece positioned on a select one of the first table and the rotary table to perform a preprogrammed machine operation.
According to yet another embodiment of the present invention, an auxiliary flush system for an electrical discharge machine includes an electrode guide having a first end portion and a first aperture arranged to receive an electrode therethrough. A dielectric fluid delivery system is arranged to deliver dielectric fluid generally within an area about the first end portion of the electrode guide, the dielectric fluid further arranged to be directed towards a workpiece so as to flush the workpiece with dielectric fluid external to the electrode.